(1) Electrophysiological characteristics of the neurones of precerebellar nuclei (e.i. inferior olive (IO) and nucleus reticularis tegmenti pontis (NRTP) were examined. The nature of the neuronal loop between these nuclei and the nucleus interpositus (IP) of the cerebellum was also studied. Intracellular recordings from these precerebellar nuclei revealed that there are excitatory loops between IP and these precerebellar nuclei. NRTP neurons have relatively higher membrane resistance, recitifying characteristics and are easily excitable by intra-cellularly applied depolarizing current. These characteristics are suited for the neurons providing background depolarization and tonic activation of the cerebellar nuclear cells. (2) input-output relationship between the substantia nigra (SN) and the caudate nucleus (Cd) in cats was studied by electrophysiological technique. stimulation of the nigro-caudate pathway induced in Cd neurons monosynaptic EPSPs followed by IPSPs. A study for identification of possible neuro-transmitter on this circuit is being conducted.